Work machines are used in earth moving operations to move material, such as dirt, rock, clay, ash, and various other materials that can become sticky when they are wet making them difficult to move with conventional dump trucks. Two types of work machines that are commonly used in the industry to perform this task are dump trucks and ejector trucks. Both types of trucks have a receptacle body to carry the material being moved. A dump truck typically raises its receptacle body to dump the load which can result in loss of stability whereas the receptacle body of an ejector truck does not raise up as the load is ejected, thereby minimizing the loss of its stability. In an ejector truck, an ejector blade is moveably mounted within the receptacle body and is coupled to a hydraulic ram or cylinder or other mechanical means which extends and retracts to move the blade through the body. Ejector trucks are useful in many applications where a traditional tilting dump truck is undesirable or impractical. For instance, if there are power lines or a low bridge or other structure located above the worksite, the ejector truck can dump its load without contacting the overhead obstruction as would a tilting dump truck. Also, an ejector truck can better maintain stability while dumping and spread material while moving, thereby reducing the spreading cost and reducing the truck cycle time making it more cost efficient. The ejector truck can also dump and spread the material more accurately than can a gravity-powered tilting dump truck, since the powered ejector blade gives the operator a great deal of control over the flow rate and distribution of the material.
A principal advantage of ejector blade machines is that the ejector blade cleans all the sticky materials out of the receptacle body. In contrast, some of the material in the receptacle body of regular dump trucks can get stuck or frozen to the sides and floor of the receptacle body. In the industry this is known as “carry back” since the material that is stuck in the receptacle body is carried in the receptacle body even after the load has been dumped. Carry back builds up thereby making conventional dump trucks inefficient since they loose load capacity which adds to the cost of operations.
Although ejector blade machines do a good job of preventing carry back inside the receptacle body, material can still get stuck and continue to build up on the ejector blade itself, thereby creating a carry back situation. This type of carry back situation can be amplified if material becomes frozen to the ejector blade during cold weather operations. There have been various attempts to solve the ejector blade carry back problem. One such prior art solution is to coat the ejector blade with a high density plastic to try to prevent material from sticking to the ejector blade. However, this solution has not been successful due to crevices in the blade and scratches in the plastic from abrasive materials that enable material adhesion due to the high amount of pressure against the ejector blade as it ejects a load.
One reason that material becomes adhered to an ejector blade is because of the large amount of pressure that the material being ejected puts on the blade as the blade pushes against and ejects the material from the receptacle body. As the blade pushes against the material, the ejector blade tends to want to twist laterally and pitch fore and aft about the longitudinal axis of the receptacle body. These tendencies are caused by the large amount of material within the body that is resisting the movement of the ejector blade as the material is being ejected. It would be desirable to minimize the twisting of the blade as it ejects material.
One solution that has been attempted to prevent carry back in regular dump trucks is described in U.S. Pat. No. 4,175,906 (Johnston). The device disclosed in the Johnston patent comprises a hydraulically powered vibrator mounted to the underside of the receptacle body. The vibrator is actuated when the receptacle body is raised above a predetermined angle. The vibrator is powered by the hydraulic system that raises and lowers the receptacle body. Although this design may work for traditional dump trucks, it does not work with trucks that have ejector blades because of the longitudinal movement of the ejector blade through the receptacle body. It would be impractical and prone to failure to have hydraulic hoses or electric cables dangling or moving through the receptacle body as the ejector blade is extending and retracting through the length of the receptacle body.